Dealing with DWI rates

“This troubling data shows us, for the first time, the scope of drugged driving in America, and reinforces the need to reduce drug abuse. Drugged driving, like drunk driving, is a matter of public safety and health. It puts us all at risk and must be prevented.” –Gil Kerlikowske, director of the office of National Drug Control Policy.

While this voluntary survey found that the percentage of drunk drivers – those with a blood alcohol concentration (BAC) of .08 or higher – has declined significantly over the last three decades, new screening techniques discovered that a lot of folks are getting behind the wheel high on a variety of illegal narcotics … especially at night. That data got the attention of safety experts throughout the federal government as it could be a serious and worrisome trend.

Yet this new survey from NHTSA is, in a way, an isolated island in a sea of activity. It represents the first time the agency took samples of “oral fluids” (which I assume to be saliva or “spit” as we all call it) and blood and then used new screening techniques to look for illegal drugs. An ongoing follow-up survey using these new detection efforts is slated to be wrapped up by 2012, so we’ll have to wait a while to see what NHTSA discovers in terms of the rate of drivers found with illegal drugs in their system.

OK, to the numbers. First, the alcohol-impairment findings:

• First, NHTSA recorded a continuing decline in the percentage of legally intoxicated drivers. In 1973, 7.5 percent of drivers had a blood alcohol concentration (BAC) of .08 or higher. By 2007, however, the rate declined to 2.2 percent. NHTSA also noted a BAC of .08 or higher is now above the legal limit in all 50 states and the District of Columbia.

• The percentage of male drivers with illegal BAC levels was 42 percent higher than the percentage of alcohol-impaired female drivers.

• Time of day made a big difference in the likelihood of drivers having illegal BACs. Looking just at Friday daytime (9:30 a.m. to 11:30 a.m. and 1:30 p.m. to 3:30 p.m.), early nighttime (10:00 p.m. to midnight), and late nighttime (1 a.m. to 3 a.m. Saturday), only 0.2% of drivers had illegal BACs during the daytime, while 1.2% had illegal BACs during the early nighttime and 4.8% had illegal BACs during the late nighttime.

• Overall, drivers were more likely to be illegally drunk during late nighttime hours (1 a.m. to 3 a.m.) than during daytime or early evening hours.

• Motorcycle riders were more than twice as likely as passenger vehicle drivers to be drunk (5.6 percent compared with 2.3 percent). Pickup truck drivers were the next most likely to have illegal BACs (3.3 percent).

Now, the illegal drugs while driving findings:

• NHTSA’s survey found 16.3 percent of nighttime weekend drivers were drug positive.The survey focused on weekend nighttime drivers and found that the drugs used most commonly by drivers were: marijuana (8.6 percent); cocaine (3.9 percent); and over-the-counter and prescription drugs (3.9 percent).

• Based on the oral fluid results, more nighttime drivers (14.4%) were drug-positive then were daytime drivers (11.0%). Based on the blood test results which were administered only at nighttime, 13.8% of the drivers were drug-positive. Using the combined results of either or both oral fluid and blood tests, 16.3% of the nighttime drivers were drug-positive.

An important point to note here: NHTSA stressed that most “psychoactive drugs” like marijuana are chemically complex molecules, whose absorption, action, and elimination from the body are difficult to predict, and considerable differences exist between individuals with regard to the rates with which these processes occur. Thus the result of these factors is that, at the current time, noted NHTSA, specific drug concentration levels cannot be reliably equated with effects on driver performance.

Alcohol, in comparison, is more predictable, said NHTSA, as a a strong relationship between BAC level and impairment has been established, as has the correlation between BAC level and crash risk.

It should also be noted that NHTSA excluded commercial vehicle drivers for logistical reasons from this survey – as a much larger area is needed to safely pull over tractor-trailers – while motorcycle operators were over-sampled, since motorcycle deaths have more than doubled over the last decade and motorcycle crashes have the highest alcohol involvement rate of any vehicle type.

The basic survey procedure involved the use of law enforcement officers to direct traffic at the survey sites, but not otherwise to interact in any way with the survey subjects, noted NHTSA. Trained data collectors solicited participation of the drivers in the survey at 300 collection sites in cities and on rural roads, offering incentives for participation, with that participation being voluntary and anonymous. Note, however, that drivers found to be impaired were not allowed to get back into their vehicles and drive away.

So what does all of this tell us? For starters, the rate of drivers impaired by alcohol operating a motor vehicle dropped significantly in over 30 years …. but it’s still a big problem. “Alcohol still kills 13,000 people a year on our roads,” stressed Transportation Secretary Ray LaHood. “So we must continue to be vigilant in our efforts to prevent drunk driving.”

Drug use by drivers is definitely worrisome, but putting NHTSA’s numbers into context is difficult. This is new research and as such is still being digested. We’ll know more as the agency wraps up its follow-on survey in 2012.

One thing is certain: the issue of DWI isn’t going away – and drunk/drugged driving leads to almost four times as many deaths on our highways than truck-car collisions. That is a startling factoid and one that needs to be remembered as we work towards reducing the annual fatalities suffered on our roadways.